Natural sources of pollutants

Key point

The contribution of natural sources to PM10 ranges from 29 percent to 55 percent of annual PM10 concentrations at urban locations.

Sea salt, pollen, dust, bushfires, and volcanoes can produce air pollutants. However, their contribution can be relatively stable (over a year) except when natural events occur, such as volcanic eruptions or bush fires.

The amount and proportion of PM10 from natural sources varies between sites, and within sites throughout the year.

From 2000 to 2012, the estimated annual average contribution from natural sources ranged from 4 μg/m3 in Blenheim to 13 μg/m3 in Dunedin, or about 18 to 63 percent of the World Health Organization (WHO) long-term guideline for PM10, respectively (see figure 27). Upper Hutt had the greatest proportion of its annual PM10 concentrations contributed from natural sources at 55 percent. Hastings had the lowest proportion at 29 percent.

These values can fluctuate from year to year. As the information presented covers different monitoring periods the results from the different sites may not be directly comparable across all sites but gives a good indication of variation.

PM10 from natural sources generally makes up a small proportion of total PM10 on peak PM10 days, but in some locations on some days it can be a major contributor (up to 90 percent) (GNS Science, 2009, 2011, & 2013). The proportion from natural sources, however, decreases during winter as contributions from home heating increase.